Frequency compensated mass flowmeter



Nov. 12, 1963 c. F. TAYLOR ETAL 3,110,180

FREQUENCY COMPENSATED MASS FLOWMETER Filed March 19, 1959 5 Sheets-Sheet3 Synchro Receiver United States Patent 3,119,130 FREQEJENQY CGMPENSATEDMAS FLGWMETER lenient F. Taylor, Lynn, Hahn R. iacintyre, Peabody, andHenry D. Oakley, Lynn, Masa, assignors to General Electric (Iompany, acorporation of New York Filed Mar. 19, E51 Ser. No. 899,599 14 Claims.(ill. 73-194) This invention relates to the minimizing of errors in amass flow -eter system and in particular, to an arrangement for use witha flowmeter to compensate for errors which result from deviations of theimpeller speed of rotation from the nominal speed at which the systemindicator has been calibrated.

Accurate measurement and control of fluid flow with reference to massmay be advantageously performed with apparatus utilizing angularmomentum phenomena. In such apparatus, the measured fluid is acceleratedto a uniform linear speed about a given axis by a fluid impeller rotatedabout that axis at a constant speed. Measurements representative of thepower required for such acceleration or representative of the power lostin predetermined deceleration of the fluid after it has been soaccelerated is used as an indicadon of mass flow characteristics.However, the electrical position signal produced by such massflow-meters is proportional not only to the mass flow rate but to theimpeller speed of rotation. In other words, the indicator scale readingswill be accurate only at the impeller speed at which the scale wascalibrated and deviations from such speed will result in indicatorerrors. It is common practice to drive the impeller of such a flowmeterfrom a synchronous electric motor. in such installations, the frequencyof the power system may vary sufiiciently to cause variations of motorspeed and thus errors of mass fiow indications through variations ofimpeller speed. Similarly, many constant speed impeller drivearrangements have speed variations of 11% or more, introducing indicatorerrors.

it is an object of the present invention to provide an improved massflow measurement apparatus wherein effects of impeller speed variationsfrom a nominal speed are automatically compensated for.

Another object of the invention is to provide an improved arrangementfor developing and utilizing the speed compensating signal in massflowmeter measurement apparatus.

Yet another object of this invention is to provide an improvedarrangement for compensating the mass flow signal for impeller speeddeviations at the indicator Inc-- tive means through use of a magnetictorque arrangement.

Further objects and advantages of the invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

In accordance wi h one form of the invention, a fluid mass rate of flowmeasuring device of the type having motive means driving the fluidthrough a flow detector is provided with a remote position telemeteringarrangement to position an indicator in accordance with the angularresponse of the mass rate of flow sensing means. The telemeteringarrangement is connected through a resilient coupling to the indicatorpointer shaft.

The indicator pointer shaft includes a member deflected therewith andlinked magnetically with a coil which develops a magnetic speedcompensating torque on the shaft in accordance with a speed deviationsignal applied to the coil. The speed deviation signal is, in turn,provided by a speed responsive circuit which produces an 2 electricsignal the magnitude and phase of which varies as the magnitude anddirection, respectively, of the impeller speed deviations from apredetermined speed at which the indicator is calibrated. The indicatorreading is thus compensated to avoid errors which would otherwise occurbecause of impeller speed deviations.

For a better understanding of this invention, reference may be had tothe following description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic representation in block diagram form of a massflowmeter system embodying the subject invention;

FIG. 2 is a schematic diagram of the frequency sensing network of FIG.1;

FIG. 3 is a schematic representation of a torque element useful in thesystem of FIG. 1;

FIG. 4 illustrates an alternative torque element coupling arrangement;

HG. 5 illustrates the preferred embodiment of the torque element of FIG.1;

FIG. 6 is the top view of the torque element shown in H6. 4 andillustrates the coil placement relative to the conductive disk;

PEG. 7 illustrates a direct current torque element suitable for use inthe system of FIG. 1;

FIG. 8 is a cross-sectional side view of the torque element of FIG. 7,taken along line AA in the direction of the arrows; and

FIG. 9 is a schematic diagram of an alternating to direct currenttransducer for use with the torque element shown in H68. 7 and 8.

Referring to FIG. 1, the fluid M to be measured passes through flowmeteror flow detector 1 via fluid conduit 2. In the flow detector 1 angularmomentum proportional to line frequency is imparted to each uni-t massof fuel by an impeller (not shown) driven by the impeller drivesynchronous motor 3. By suitable means well known in the art, such as byrecovering the angular momentum, a mechanical torque is developedproportional to the product of mass 'fiow rate and line frequency.

The operation and general construction of the flow detector 1 isexplained in more detail in the copending patent application, Serial No.797,177, filed March 4, 1959, now Patent No. 3,084,544, in the name ofClement F. Taylor, and assigned to the same assignee as the subjectinvention.

The mechanical deflection 0 of flow detector 1 caused by the fluid flowM is coupled by shaft 4 to the rotor (not shown) of synchro transmitter5 which is excited from the power source line frequency to produce anelectrical signal 0 at the stator (not shown) representing a shaftrotation or angular deflection 0 proportional to the product of massflow rate and frequency.

The flow detector 1, impeller drive 3, and synchro transmitter 5 may beconveniently packaged'in a single unit located at the fuel flow linewhile the remainder of the system may be physically located remotetherefrom and contained within a second unit.

The electrical signal 0., developed by the stator winding (not shown) ofsynchro transmitter 5 is connected via cable .6 to the stator winding ofsynchro receiver 7. The rotor (not shown) of synchro receiver 7 isconnected to the line voltage e so that the synchro receiver 7 repeatsaccurately the position of the synchro transmitter 5. For a morecomplete description of the theory of synchro construction and operationreference may be had to Section 59 (a) of the publication Radar SystemFundamentals (NAVSHIPS 900,017) published by the Bureau of Ships, NavyDept., in April 1944.

The rotor of synchro receiver 7 is mechanically coupled to torqueelement 8 by shaft 9 to produce a rotation of 3 indicator shaft or driveconnection it proportional to the product of mass flow rate andfrequency. The arrangement described thus far is a synchro positioningsystem to position the shaft 16 in accordance with the angulardeflection 9 of flow detector 1.

The torque exerted on the rotor of synchro receiver 7 is proportional tothe sine of the angle between the axis of the field induced by thesignal and the magnetic axis of the rotor. However, since the entirerange of operation of the subject system is confined to relatively smallangular deflections, the sine curve approximates a straight line and thetorque versus deflection characteristic is substantially linear.Therefore, non-linearities are not introduced by the synchro torquecharacteristic.

An indicator 11 is coupled to shaft 10 and is calibrated in mass flowrate at the nominal line frequency which is shown in FIG. 1 as 400cycles. Since the pointer deflection of indicator 11 is proportional tothe products of mass flow rate and frequency, indications atfrequencsies other than nominal will be in error an amount proportionalto the line frequency deviation from nominal. The above discussion is interms of line frequency deviations since the line frequency of thedisclosed system determines the speed of synchronous impeller drivemotor 3 driving the impeller of fiowmeter 1; However, it should beappreciated that the subject invention can be utilized with any type ofimpeller drive by deriving an electrical signal from the impeller drivesystem which is proportional to the speed of the impeller. This may beconveniently accomplished through use of a tachometer generator coupledto the impeller drive. Therefore, for purposes of the subjectdiscussion, line frequency deviations may be equated to impeller speeddeviations.

In order to compensate for variations of line frequency, a compensatingelectrical signal is developed by fre quency sensing network or detector12 to produce a compensating torque in torque element 8 to modify andcorrect the mass flow rates of indicator 11.

FIG. 2. shows a suitable frequency sensing network 12, although thenetwork could be of the type disclosed in the aforesaid Taylorapplication. Referring to FIG. 2, the line voltage e is applied toopposite junctions 14 and 15 of the bridge circuit which is of thegeneral type referred to as Wien bridge. In accordance with theoperation of a Wien bridge, and as set forth in detail in Section 10-4of the text book Basic Electrical Measurements, by Melville B. Stout,published by Prentice-Hall, Inc. of New York in 1950, the bridge willbalance at a particular frequency. The frequency at which the bridgewill balance is determined by the components thereof and is made to bethe nominal line frequency. The output voltage e; appearing across theremaining bridge junctions 16 and 17, is an alternating signal of amagnitude proportional to the frequency deviation from nominal thatreverses phase as the frequency passes through the nominal frequency.One of the bridge arms comprises the resistor 18 and capacitor 19connected'in series and the adjacent bridge arm connected to junction 14comprises resistor 20 and capacitor 21 connected in parallel. Whenresistors 18 and 20 are of equal magnitude and the arm opposite theparallel combination comprises 7 a resistor 22 having a resistance twicethat of resistor 23 in the remaining arm, the output compensating signala may be conveniently represented by the following relationship:

where:

f=line frequency. f =nominal frequency (460 c.p.s.).

The torque element 8, which converts compensating signal e; to acompensating torque is shown in more detail in FIG. 3. Referring to FIG.3, the synchro receiver 7 is coupled through resilient coupling orspring 24 and drive shaft it) to the pointer 13 of indicator 11 toproduce an angular deflection proportional to that of the flowdetector 1. Electrically conductive rotor disk 26 is rigidly mounted onshaft 10 for deflection therewith and links the magnetic field producedby current flow in the coils 27 and 28 mounted on opposite sides of thedisk 26. Coils 27 and 28 are wound on legs 29 and 30 of the highpermeability magnetic member 31 which surrounds disk 26 and form an airgap 32 in which the disk deflects. Coil 27 is a reference coil energizedby the line voltage e through capacitor 45 to produce a current flowtherein proportional ot line voltage, while coil 28 is a control coilenergized by the compensating voltage e to produce a current flowtherein in accordance with the frequency deviation. The magnetic fieldsproduced by the coils 27 and 28 provide a resultant magnetic field whichhas a component that appears to move in a tan gential direction throughthe air gap, that is at right angles to the axis of rotation of shaft 10and to a radius drawn from that axis. The magnitude of this movingmagnetic field component is proportional to the compensating signal eacross the control coil, and the resultant compensating torque exertedon the disk 26 and shaft 10 is therefore proportional to the deviationof line frequency from nominal. The torque is produced by theinteraction of the magnetic fluxes in the air gap 32 and the eddycurrents in the disk 26. V

The coupling spring 24 is interposed between the rotor output shaft 9 ofsynchro receiver 7 and the indicator drive shaft or mechanical driveconnection in in order to make the torque developed by the synchroreceiver of the same order of magnitude as that of the torque element 3.Otherwise the torque developed by synchro receiver 7 may be so large asto require a compensating torque greater than the capabilities of torqueelement 8 without power amplification. Also, such as arrangement enablesthe direct application of the compensating torque to the indicator driveshaft 10 independent of the torque gradient of the synchro receiver 7.It is also possible to use known electrical instrument techniques toenable selective adjustment of the spring parameters.

An "alternate torque element coupling arrangement is shown in FIG. 4.Referring to FIG. 4, the synchro receiver rotor shaft 9 is axiallyaligned with but spaced from indicator shaft 10 and spiral spring 24 hasits inner end secured to shaft 9. The outer end of spring 24 is securedthrough connecting member 33 to gear 48. The torque element 8 shownschematically and including conductive rotatable disk 26 may then beconstructed as an integral unit and the shaft 47 supporting the disk iscoupled to gear 48 through connecting gear 49.

The electrically conductive disk 26 is made of zero temperaturecoefiicient material and is shaped such that as the disk rotates in thedirection corresponding to increasing flow rate a continuously varyingarea is exposed to the magnetic field of the stator to produce a torquethat is proportional to mass flow rate. 26 is shown in detail in FIG. 6,hereinafter described.

The arrangement of the reference coil 27 and control coil 28 in thetorque element 8 of FIG. 3 will produce an unwanted torque when thefrequency deviation and hence the current flow in the control coil 28are zero since there is current flow in the reference coil under alloperating conditions. A preferred arrangement of coils 2:7 and 28relative to the conductive disk 26 is shown in FIGS. 5 and 6. Referringto FIGS. 5 and 6, it will be seen that the general magneticconfiguration is similar to that of an induction watthour meter.Magnetic cores 34, 35 and 36- are constructed of laminated silicon steeland form closed magnetic circuits having end portions above and belowthe disk 26 and forming air gaps in which the disk may rotate. The airgaps 37, 38. and 39 respectively, are perpendicular to the disk 26 andextend in a direction parallel to shaft 1%. Magnetic core 35 has a leg4% below disk 26 which extends parallel to The shaping of the disk theshaft with reference coil 27 being wound about the leg. Control coil 28is in two portions electrically connected in series through lead 41 withone half or portion 28a wound upon leg 42 of magnetic core 34 and theother half or portion 28b wound upon leg 43 of magnetic core 36. Thelegs as, 42., and 43 are contiguous to one another and the magneticcores 34, 35 and 36 are positioned such that air gaps 37, 38 and 39 aredisplaced from shaft 10 and in the region of the circumferential edge6i) of disk 26 at low flow rates. As best illustrated by FIG. 6, themagnetic member 35 extends in a radial direction from shaft 1t Whilemagnetic members 34 and 36 are perpendicular to and on opposite sides ormember 35 and extend generally in a tangential direction to disk 26.

Disk 26 is rigidly fastened to shaft 1% and deflects within the air gaps37, 38 and 3? to provide a compensating torque in accordance with thesignal e When the frequency deviation of the line frequency from nominalis zero, that is the line frequency is 400 cycles per second, nocompensation torque is required. No torque will be produced by thecompensating coils 23a and 28b due to a since 2; is Zero at the nominalfrequency. The torque set up by current flow in reference coil 27 willbe in a radial direction and no resultant rotational torque upon shaftit} will be produced thereby. The torques produced by the voltagesinduced in coils Z-Sa and 2312 by coil 27 will have no effect upon theshaft ill since the coils are symmetrical and connected such that thefluxes produced through mutual inductance balance one another.

Since e is proportional both in magnitude and phase to the frequencydeviation, the resultant current flow in coils 28a and 28b is similarlyrelated to the frequency deviation. The fluxes produced by coils 23a and28b in combination with the flux produced by reference coil 27 producesan angular deflection of disk 26 to compensate the indicator 11 inaccordance with the f equency deviation. Variable resistor 44 in serieswith coils 23a and 28b enables selective adjustment of the compensatingefiect and is adjusted at the time of calibration of indicator 11.

Capacitor 45 in series with the reference coil 27 reduces the voltamperes drawn from the supply line 2 and may conveniently have apositive temperature coeflicient to compensate for temperature etfecisof the system. In addition, the current variations which result in thereference coil 27 with variations of line 'frequency because ofcapacitor 45 compensate for variations of current flow in the controlcoils 23a and 2812 due to variations of line frequency.

The direction of rotation or" disk 25 for increasing flow rate isindicated by the arrow 45 in PEG. 6. If disk 26 were to have a circularshape, the compensating torque produced for a given frequency deviationwould be the same for all angular positions of the disk. In order tohave the compensating torque proportional to scale position, the disk 26is made in the shape of a cam that extends furthest into the air gap atthe full scale position of indicator =11 and extends the least into theair gap at the zero position. The correcting torque is thus made notonly proportional to the irequency deviation but also proportional tothe scale position of the indicator. The torque required to correct fora given frequency deviation is proportional to the scale position for agiven frequency deviation since less torque is required, for example, tocorrect for a given frequency deviation at half scale position than isrequired at full scale position. Relating torque to scale position isnot necessary if the flow rate of a particular system varies Within acomparatively narrow range.

During operation, if the line frequency is the nominal frequency of 400cycles per second, the frequency compensating voltage e is zero and thetorque element 8 exerts no torque on the shaft 18 and no compensation isapplied to indicator 11. If the frequency. should decrease, for exampleto 380 cycles, the position of indicator pointer 13 without compensationwould be approximately 5% too low. However, the torque element 8 exertsa torque on shaft 10 to urge the pointer 13 to the position it would beif the line frequency were 400 cycles instead of 380 cycles. Likewisewhen the frequency increases from nominal, for example to 420 cycles,the torque exerted by the element 8 is in the proper direction to urgethe indicator shaft down scale to the position it would take if the linefrequency was nominal.

Expressed mathematically, the torque T developed in the torque elementis:

where: 0=rotation of indicator from zero. K =combined constant of torqueelement and frequency network.

The torque T developed by the synchro receiver 7 may be expressedmathematically as:

2 2( where: K =synchro receiver torque constant.

qb=angular rotation of synchro transmitter from zero.

and

6K2 lf Therefore, the rotation of the indicator becomes proportional tomass flow rate and independent of frequency since the angular rotationof the synchro transmitter from zero, is proportional to mass rate offlow and frequency.

A direct current torque element can be used in place of the alternatingcurrent torque element 8. Direct current of proper magnitude and phasesensitivity or polarity e can be derived from the compensating signal ethrough a rectifying arrangement. This current can be converted to afrequency compensating torque in an arrangement such as that shown inFIGS. 7 and 8. Referring to FIGS. 7 and 8, the direct current torqueelement 8' includes a C-shaped permanent magnet 5s rigidly mounted onshaft 1i? and oriented along the shaft such that the air gap 51 extendsradially relative to shaft lit). Toroidal coil 52 passes through the gap51 and surrounds the shaft 19 to provide clearance for deflection of theshaft and the permanent magnet Sit. The toroidal coil 52 isnon-uniformly or non-linearly wound upon core 53 so that the spacingbetween the adjacent turns decreases with the angular deflection aclock-wise or increasing flow rate direction as indicated by arrow 54from the zero flow rate position shown. The number of turns per inch andthe resultant compensating torque produced by the interaction hetweenthe permanent magnet 5d and the magnetic field set up by the toroidalcoil 52 is thus made proportional to the angular deflection of shaft lllor the mass low rate and also to the frequency deviation as representedby the current flow in coil 52.

instead of altering the number of turns per inch of coil 52, the coilflux could be made proportional to mass flow rate by using a uniformspacing between turns with a core 53 that increases in diameter withangular deflection of the magnet that is, in the direction of arrow 54.Since the torque produced is proportional to the coil diameter, thedesired torque relationship to mass flow rate will be realized.

In order to insure that no compensating torque is developed at zero flowrates a portion of coil 52 may be omitted in the region of zero flowrate. Alternatively, a small section of coil 52 in the region betweenfull scale and zero flow rate position can be Wound in a reversedirection and shunted by a variable resistor to produce a selectivelyadjustable reverse torque on the magnet to enable an adjustment for zerotorque at zero flow rate.

A linear voltage transducer, for the conversion of the alternatingsignal e provided by the output of the frequency sensing network 12 to adirect current voltage suitable for use in torque element 8' is shown inFIG. 9. Referring to FIG. 9, the line voltage 2 is coupled throughtransformer 55 to opposite junctions of rectifier bridge 56 while theoutput voltage is taken across the remaining junctions. The frequencycompensating signal e; is applied between the center tap 57 of thesecondary of transformer 55 and the junction between resistors 58 and 59which shunt the output junctions of rectifier bridge 55. The outputvoltage e which is the input to coil 52 of the torque element 8 providedby the diode switching or cornmutating action of the rectifier bridge 56is a direct current voltage, the amplitude of which is proportional tothe frequency deviation and the polarity of which is related to thedirection of the frequency deviation signal from nominal.

Therefore, while particular embodiments of the subject invention havebeen shown and described herein, they are in the nature of descriptionrather than limitation, and it will occur to those skilled in the artthat various changes, modifications and combinations may be made withinthe province of the appended claims without departing either in spiritor scope from this invention in its broader aspects.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. For use in a fluid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a source of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportional to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, a first shaft, meansto position said first shaft solely in response to said first signal, anindicator having a drive shaft, said first shaft being connected toposition said drive shaft through a torsionally resilient coupling, anindicator compensator comprising, means to produce a second signalproportional to the magnitude and direction of the frequency deviationof said A.-C. line voltage from said nominal frequency, and magnetictorque means connected to said drive shaft independently of saidresilient coupling to modify the position of said indicator drive shaftsolely in response to said second signal and compensate the indicatorfor speed variations of said motive means which are due to frequencyvariations of said A.-C. line voltage, said torque means including acoil connected to be enersource of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportional to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, a first shaft, meansto position said first shaft solely in response to said first signal, anindicator having a drive shaft, said first shaft being connected toposition said drive shaft through a torsionally resilient coupling, anindicator compensator comprising, means to produce a second signalproportional to the magnitude and direction of the frequency deviationof said A.-C. line voltage from said nominal frequenc and magnetictorque means connected to said drive shaft independently of saidresilient coupling to modify the position of said indicator drive shaftsolely gized solely by said second signal producing means for adeveloping a magnetic field in response to said second signal, at leasta portion of said drive shaft being linked by said magnetic field.

2. For use in a fluid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a in response to said second signal and compensatethe indicator for speed variations of said motive means which are due tofrequency variations of said A.-C. line voltage, said torque meansincluding a coil connected to be energized solely by said second signalproducing means for developing a magnetic field in response to saidsecond sig- 7 nal, at least a portion of said drive shaft being linkedby said magnetic field, the amount of linking flux produced by any givenmagnitude of said second signal varying in accordance with the positionof said indicator drive shaft.

3. For use in a fluid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a source of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportional to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicator arrangement including means to develop a first signal inaccordance with the response of the sensing means, a first shaft, meansto position said first shaft solely in response to said first signal, anindicator having a drive shaft, said first shaft being connected toposition said drive shaft through a torsionally resilient coupling, anindicator compensator comprising, means to produce a second signalproportional in magnitude and phase to the magnitude and direction,respectively, of the frequency deviation of said A.-C. line voltage fromsaid nominal frequency, and magnetic torque means connected to saiddrive shaft independently of said resilient coupling to modify theposition of said indicator drive shaft solely in response to said secondsignal, said torque means including an electrically conductive diskconnected to said drive shaft, and a coil connected to be energizedsolely by said second signal producing means to produce a magnetic fieldwhich links said conductive disk.

4. For use in a fluid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a source of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportioned to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, means to position anindicator in accordance with said first signal, an indicator compensatorcomprising, means to produce a second signal proportional in magnitudeand phase to the magnitude and direction, respectively, of the frequencydeviation of said A.-C. line voltage from said nominal frequency, andmagnetic torque means to modify the position of said indicator inresponse to said second signal, said torque means including anelectrically conductive disk connected to said positioning means, a coilconnected to be energized in accordance with said second signal toproduce a first magnetic field, and a second coil connected to beenergized by said source of A.-C. line voltage to produce a secondmagnetic field which links said first mag netic field to produce aresultant field which links said conductive disk to develop a torquethereon, and compensate the indicator for speed variations of saidmotive means which are due to frequency variations of said A.-C. linevoltage.

5. For use in a fluid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a source of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proprotioned to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, means to position anindicator in accordance with said first signai, an indicator compensatorcomprising, means to produce a second sigial proportional in magnitudeand phase to the magnitude and direction, respectively, of the frequencydeviation of said A.-C. line voltage from said nominal frequency, andmagnetic torque means to modify the position of said indicator inresponse to said second signal, said torque means including anelectrically conductive disk extending radially from said positioningmeans for deflection therewith, and a coil connected to be energized inaccordance with said second signal to produce a first magnetic field,and a second coil connected to he energized by said source of A.-C. linevoltage to produce a second magnetic field which links said firstmagnetic field to produce a resultant field which links said conductivedisk to develop a torque thereon, and compensate the indicator for speedvariations of said motive means which are due to frequency variations ofsaid A.-C. line voltage, said second coil being wound about a core whichis positioned radially to the axis of rotation of said disk, and saidfirst coil being wound about a core which is positioned perpendicular tosaid second coil.

6. For use in a fluid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a source of a A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportional to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, means to remotelyposition an indicator in accordance with said first signal, an indicatorcompensator comprising, means to produce a second signal proportional inmagnitude and phase to the magnitude and direction, respectively, thefrequency deviation of said A.-C. line voltage from said nominalfrequency, and magnetic torque means to modify the position of saidindicator in response to said second signal, said torque means includingan electrically conductive disk extending radially from said positioningmeans for deflection therewith, a first coil connected to be energizedby said source of A.-C. line voltage, a pair of coils removed from saidfirst coil, said pair of coils being connected in series and energizedby said second signal, said coils being located such that the resultantof the magnetic fields produced upon energization thereof links saidconductive disk to develop a torque thereon to compensate the indicatorfor speed variations of said motive means which are due to frequencyvariations of said A.-C. line voltage, and said disk being shaped sothat the magnetic torque developed is proportional to the disk rotation.

7. For use in a fluid mass rate of flow measuring apparatus of the typehavin a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a source of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportional to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, means to remotelyposition the indicator in accordance with said first signal andincluding a resilient coupling between said positioning means and theindicator drive, an indicator compensator comprising, means to produce asecond signal proportional in magnitude and phase to the magnitude anddirection, respectively, of the frequency deviation of said A.-C. linevoltage from said nominal frequency, and magnetic torque means coupledto said indicator drive to modify the position of said indicator inresponse to said second signal, said torque means including anelectrically conductive disk connected to said drive for rotationtherewith, a first coil connected to be energized by said source ofA.-C. line voltage, a pair of. coils removed from said first coil, saidpair of coils being connected in series and energized by said secondsignal, said coils being located such that the resultant of the magneticfields produced upon energization thereof links said conductive disk todevelop a torque thereon to compensate the indicator for speedvariations of said motive means which are due to frequency variations ofsaid A.-C. line voltage, and said disk being shaped such that themagnetic torque developed is proportional to mass flow rate.

8. For use in a fluid mass rate of flow measuring appanatus of the typehaving a fluid mass rate of flow detcctor adapted to conduct the flowingfluid and including a source of A.-C. line voltage of a nominalfrequency, motive means energized by said source of A.-C. line voltage,the speed of said fluid motive means being proportional to the frequencyof said A.-C. line voltage, and sensing means responsive to the productof mass rate of flow and speed of said motive means, an indicatingarrangement including means to develop a first signal in accordance withthe response of the sensing means, a first shaft, means to position saidfirst shaft solely in response to said first signal, an indicator havinga drive shaft, said first shaft being connected to position said driveshaft through a torsionally resilient coupling, a compensator forvariations of speed of said motive means which are due to frequencyvariations of said A.-C. line voltage comprising, means to produce asecond electrical signal proportional in magnitude and phase to themagnitude and direction, respectively, of the frequency deviation ofsaid A.-C. line voltage from said nominal frequency, and magnetic torquemeans connected to said drive shaft independently of said resilientcoupling to modify the position of said indicator drive shaft solely inresponse to said second signal, said magnetic torque means including afirst member of magnetic material and a second electromagnetic memberconnected to be energized solely by said second signal, one of saidmembers being connected to said drive shaft to move in response todeflections of said indicator drive shaft and the other of said membersbeing in a fixed position, the magnetic field produced by saidelectromagnetic member linking said first member.

9. For use in a fluid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detest-or adapted to conduct theflowing fluid and including a source of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportional to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, means to remotelyposition an indicator in accordance with said first signal, an indicatorcompensator comprising, means to produce a second signal proportional inmagnitude and phase to the magnitude and direction, respectively, of thefrequency deviation of said A.-C. line voltage from said nominalfrequency, and magnetic torque means to modify the position of saidindicator in response to said second signal, said torque means includingan electrically conductive disk connected to said positioning means fordefiection therewith, a first coil connected to be energized by saidsource of A.-C. line voltage, a pair of coils removed from said firstcoil, said pair of coils being connected in series and energized by saidsecond signal, and said coils being located such that the resultant ofthe magnetic fields produced upon energization thereof links said diskto develop a torque thereon to compensate the indicator for speedvariations of said motive means which are due to frequency variations ofsaid A.-C. line voltage, said pair of coils being connected such thatthe torque produced thereby from currents induced therein by said firstcoil cancel each other.

10. For use in a fiuid mass rate of flow measuring apparatus of the typehaving a fluid mass rate of flow detector adapted to conduct the flowingfluid and including a source of A.-C. line voltage of a nominalfrequency, fluid motive means energized by said source of A.-C. linevoltage, the speed of said fluid motive means being proportional to thefrequency of said A.-C. line voltage, and sensing means responsive tothe product of mass rate of flow and speed of said motive means; anindicating arrangement including means to develop a first signal inaccordance with the response of the sensing means, a first shaft, meansto position said first shaft solely in response to said first signal, anindicator having a drive shaft for driving said indicator, said firstshaft being connected to position said drive shaft through a torsionallyresilient coupling, an indicator compensator comprising, means toproduce a second signal proportional to the magnitude and direction ofthe frequency deviation of said A.-C. line voltage from said nominalfrequency, and magnetic torque means connected to said drive shaftindependently of said resilient coupling to modify the position ofsaid'indicator drive shaft solely in response to said second signal andcompensate the indicator for speed variations of said motive means whichare due to frequency variations of said A.-C. line voltage, said torquemeans including a coil connected to be energized solely by said secondsignal producing means for developing a magnetic field in response tosaid second signal, at least a portion of said drive shaft being linkedby said magnetic field, the amount of linking flux produced by any givenmagnitude of said second signal varying in accordance with the positionof said indicator drive shaft.

11. The combination of claim 10 in which said second signal producingmeans produces a direct current signal, and said portion of said driveshaft comprises a magnet which is linked by the magnetic field createdby said coil.

12. The combination of claim 11 in which said magnet is a permanentmagnet.

13. The combination of claim 12 in which said coil is stationary andsurrounds said drive shaft in such a Way that the magnitude of the fieldlinking said permanent magnet, for any given value of signal applied tosaid coil, varies as the position of said drive shaft varies over theflow range of the system.

14. The combination of claim 13 in which said coil is toroidal in shapeand has a nonlinear winding.

References Cited in the file of this patent UNITED STATES PATENTS2,914,944 Ballard Dec. 1, 1959 2,914,945 Cleveland Dec. 1, 19592,975,634 Rose Mar. 21, 1961

1. FOR USE IN A FLUID MASS RATE OF FLOW MEASURING APPARATUS OF THE TYPEHAVING A FLUID MASS RATE OF FLOW DETECTOR ADAPTED TO CONDUCT THE FLOWINGFLUID AND INCLUDING A SOURCE OF A.-C. LINE VOLTAGE OF A NOMINALFREQUENCY, FLUID MOTIVE MEANS ENERGIZED BY SAID SOURCE OF A.-C. LINEVOLTAGE, THE SPEED OF SAID FLUID MOTIVE MEANS BEING PROPORTIONAL TO THEFREQUENCY OF SAID A.-C. LINE VOLTAGE, AND SENSING MEANS RESPONSIVE TOTHE PRODUCT OF MASS RATE OF FLOW AND SPEED OF SAID MOTIVE MEANS; ANINDICATING ARRANGEMENT INCLUDING MEANS TO DEVELOP A FIRST SIGNAL INACCORDANCE WITH THE RESPONSE OF THE SENSING MEANS, A FIRST SHAFT, MEANSTO POSITION SAID FIRST SHAFT SOLELY IN RESPONSE TO SAID FIRST SIGNAL, ANINDICATOR HAVING A DRIVE SHAFT, SAID FIRST SHAFT BEING CONNECTED TOPOSITION SAID DRIVE SHAFT THROUGH A TORSIONALLY RESILIENT COUPLING, ANINDICATOR COMPENSATOR COMPRISING, MEANS TO PRODUCE A SECOND SIGNALPROPORTIONAL TO THE MAGNITUDE AND DIRECTION OF THE FREQUENCY DEVIATIONOF SAID A.-C. LINE VOLTAGE FROM SAID NOMINAL FREQUENCY, AND MAGNETICTORQUE MEANS CONNECTED TO SAID DRIVE SHAFT INDEPENDENTLY OF SAIDRESILIENT COUPLING TO MODIFY THE POSITION OF SAID INDICATOR DRIVE SHAFTSOLELY IN RESPONSE TO SAID SECOND SIGNAL AND COMPENSATE THE INDICATORFOR SPEED VARIATIONS OF SAID MOTIVE MEANS WHICH ARE DUE TO FREQUENCYVARIATIONS OF SAID A.-C. LINE VOLTAGE, SAID TORQUE MEANS INCLUDING ACOIL CONNECTED TO BE ENERGIZED SOLELY BY SAID SECOND SIGNAL PRODUCINGMEANS FOR DEVELOPING A MAGNETIC FIELD IN RESPONSE TO SAID SECOND SIGNAL,AT LEAST A PORTION OF SAID DRIVE SHAFT BEING LINKED BY SAID MAGNETICFIELD.